When the men and women aboard a modern submarine hear the command to dive, they can take a measure of comfort in the fact that no US sub has been lost in nearly 40 years, though it’s been said that the sea is a more hostile environment than space. The tragedies of former disasters have not been forgotten or squandered and the Navy has been extremely motivated to find ever more effective ways to prevent them. We’ll examine sub disasters to discover what caused them and what they’ve taught us. And as we explore the early history of the submarine–including a sub used in the American Revolution and one used in the Civil War–we follow a modern crew using submarine simulators to train for disasters, study subs in the nuclear age, and explore state-of-the-art rescue technology.